What telescope do I need to see Didymos?

At magnitude 14.3, Didymos is a challenging target that needs at least an 8-inch (200 mm) telescope and dark skies.

Didymos — Near-Earth Object in Ophiuchus

65803 Didymos, 1996 GT

Magnitude 14.3^m NearEarthObject Ophiuchus (Oph) Visible

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Properties

Magnitude 14.3

Description

Type: Near-Earth Object

Distance: 1.643 AU

Orbital Period: 768.9 days

Diameter: 1 km

Features: Equatorial ridge typical of fast rotators; rubble-pile structure

Binary asteroid system: a roughly 780 m S-type primary with a small ~150 m moonlet (Dimorphos). Target of NASA's DART mission, the first planetary-defence test, which impacted Dimorphos in September 2022 and shortened its orbital period by ~33 minutes. ESA's Hera mission visits in late 2026.

Position & Identifiers

RA 16h 34m 27.2s

Dec -24° 40' 15.4"

Constellation Ophiuchus (Oph)

Catalog Didymos

Physical Properties

Diameter 1 km

Mass 5.28e11 kg

Albedo 0.15 (15% reflected)

Rotation 2.3 hours

Surface Equatorial ridge typical of fast rotators; rubble-pile structure

Angular Size 0.0″ (current)

Orbital Properties

Semi-major Axis 1.6426 AU (245.7 million km)

Eccentricity 0.3832

Inclination 3.41°

Orbital Period 2.11 years

Distance 1.228 AU (10.2 light-min)

Elongation 83.8° Moderate

Brightness Forecast (next 12 months)

Apparent magnitude as Earth–asteroid distance changes through the year. The peak marks the brightest moment in the window — usually around opposition, when the asteroid is closest and fully illuminated.

Computed from JPL orbital elements via m = H + 5·log₁₀(r·Δ). Phase-function correction is omitted, so curves trace distance variation only — accurate within a few tenths for main-belt asteroids; coarse for fast-moving NEOs near Earth.

Observing Tips

Visibility Large telescope only at close approach

Where to Look Near-Earth asteroid (Apollo group); inner-Earth crosser

Notes Binary asteroid system: a roughly 780 m S-type primary with a small ~150 m moonlet (Dimorphos). Target of NASA's DART mission, the first planetary-defence test, which impacted Dimorphos in September 2022 and shortened its orbital period by ~33 minutes. ESA's Hera mission visits in late 2026.